[Gimp-user] jpeg loss on multiple export

[Gary Aitken <gimp dreamchaser org>]

At the risk of committing a mailing list etiquette fopah...
I'm reposting as I got no response and I am hoping one of the developers 
can actually shed light on this:

On 5/3/2012 8:15 AM, Jay Smith wrote:

> Jonathan, I hope that you realized that when editing a JPG, repeatedly
> saving/exporting to JPG (your step 4) reduces the quality (actually
> compresses / deletes data).

GIMP doesn't reload the file after exporting, does it?
If not, then the image in the GIMP's buffer should be the same high 
quality image it was prior to the export.
Given that, as long as you don't exit the GIMP or reload the image from 
the exported file, multiple exports to a lossy format shouldn't cause 
loss of quality.

For example, if you do an export to jpeg and compress down to 15%, with 
the preview option set you can clearly see the loss of quality in the 
written image.  However, when the export is complete, the image in the 
buffer reverts to the high quality it was prior to the export.

This implies multiple exports to a lossy format should *not* result in 
loss of image quality.  However, *re-loading* an image previously saved 
to a lossy format and then exporting again will result in degradation.

Is there something I'm missing?

Gary